Acoustic wave devices using a piezoelectric thin film resonator have been used as filters in wireless devices, for example. The piezoelectric thin film resonator has a structure designed to have a lower electrode and an upper electrode facing each other across a piezoelectric film. A resonance region is a region in which the lower electrode and the upper electrode face each other across the piezoelectric film. Japanese Patent Application Publication Nos. 2012-165288 and 2011-71913 disclose forming a load film in a part in the resonance region.
Spurious may occur at frequencies lower or higher than the resonance frequency in the piezoelectric thin film resonator. For example, when a filter is formed by using a piezoelectric thin film resonator in which spurious occurs, a ripple is formed in the passband.